The all important OM (AUM) Mantra Meditation to open the powerful Third Eye Chakra.
This meditation uses the AUM Mantra, along with Gyan Mudra (finger position of wisdom) and Shambhavi Mudra to activate and open the Third Eye.
This meditation is particularly effective in opening the Third Eye as it uses the seed sound (Beej Mantra) OM for stimulating the Third Eye and helping it open rapidly.
You can get full details on timings, benefits, cautions, modification, etc in the following free article - http://anmolmehta.com/blog/2007/05/03/ajna-chakra-meditation-technique-3rd-eye-free-guided-meditation-book-for-daily-practice/.